In the exploration and production of hydrocarbons, it is desirable that the properties of the subterranean formation, such as resistivity of the subterranean formation surrounding a wellbore, be detected. Resistivity tools measure a wellbore resistivity, and the resistivity measurements may then be utilized to obtain a wellbore wall image. When measuring the micro-resistivity of a low-resistivity subterranean formation surrounding a wellbore, an unknown standoff distance between the resistivity tool and the surrounding subterranean formation can lead to errors in estimating the resistivity of the surrounding subterranean formation. Such errors may be exacerbated with the larger standoffs associated with some tools that are operable for continuous acquisition of formation resistivity data.
Electrical wellbore imaging revolves around using an adequate operating frequency so that an impedance of the mud in the wellbore is sufficiently reduced, thereby allowing measurement of the formation resistivity. A challenge remains with respect to removing the mud contribution from the measurement especially when the mud is an oil-based mud, which is very resistive. Various processing techniques have been proposed to remove the mud contribution from the measurement. These methods are based on approximating a formation impedance measurement by an equivalent circuit including an impedance in series. The aforementioned technique, however, has limited applicability to smaller standoff distances and/or poor resolution of sensing formation impedance with a conductive pad in series with a current-sensing circuit element.